The world’s lack of progress in building toilets and ending open defecation is having a “staggering” effect on the health, safety, education, prosperity and dignity of 2.5 billion people, the UN deputy secretary general, Jan Eliasson, has warned.

“Sanitation is cross-cutting: if you make progress on sanitation, then you dramatically improve the achievement of at least four other goals,” he told the Guardian.

“One of the main reasons for child mortality is diarrhoea and dysentery because of bad water and a lack of sanitation. You get a much better way of working with maternal health issues: I can’t tell you how many women are dying in childbirth because of a lack of clean water. You’ll affect education, because people can’t go to school when they have these huge problems, and you will have productive people who can go to work.”

Eliasson said building toilets for women was fundamental to gender equality, education – and safety. “In Africa, in particular, there is an unfortunate situation where girls don’t have toilets in their schools,” he said. “It’s very easy to arrange them for the boys, but girls require more privacy. And then you get into the area that we saw in that horrible example in India, when the girls went out at night and were raped and killed. This is done in innumerable cases: men preying on young girls who are going out like that.”

According to the UN, 2.5 billion people still lack “improved sanitation facilities” – defined as ones that “hygienically separate human excreta from human contact”, down only 7% since 1990, when 2.7 billion lacked access, and more than a billion people – most of whom live in rural areas – have to defecate in gutters, behind bushes or into water.

More people have access to mobile phones than toilets, it says.

“This, for me, is one of the most drastic and sad examples of the loss of dignity: allowing 1.1 billion people in 22 countries to practise open defecation,” said Eliasson. “Apart from the human dignity aspect, there is the health aspect and the environmental aspect.”

Eliasson, a former chairman of WaterAid Sweden, said he was driven to speak out by memories of the children he had seen die from diarrhoea, dysentery and dehydration. “It’s a very concrete challenge and it’s not rocket science,” he said. “We need to do something about it.”

Although he was heartened to see governments belatedly waking up to the importance of sanitation, progress has been far too slow. The millennium development goal (MDG) on sanitation – which aims to halve the proportion of the population without sustainable access to basic sanitation by the end of next year – is unlikely to be met, he said.

“I think we have seen progress on water, although there are still 780 million people without safe water. But I am sad to say that we have not seen the same pace of progress on sanitation. On the contrary, I would say the sanitation goal is one of the most lagging of all the goals, and that is why we have tried our best to speed up the work for achieving it by the end of next year.” He said the fact that sanitation and water are likely to have their own standalone place among the sustainable development goals (SDG), which will succeed the MDGs, was “a sad confirmation” of international inaction. But he said he was at least encouraged to see it was already a high priority; during the formulation of the MDGs it had to be added by a specific resolution.

Age-old taboos around toilets and defecation, he added, were finally breaking down. He pointed to India, where the new prime minister, Narendra Modi, tackled the issue during his election campaign, calling on the nation to build “toilets first and temples later”.

In sub-Saharan Africa, too, the issue is increasingly on the agenda. In July, the prime minister of the Democratic Republic of the Congo – a state blighted by sexual violence – told the Guardian provision of toilets had a direct bearing on education and gender equality. “It’s not just about classrooms, you also need toilets, and providing toilets for boys and toilets for girls limits the risk of girls being attacked when they go to the toilet,” said Augustin Matata Ponyo. “And that provision encourages parents to send their children to school, because they feel reassured that those toilets mean their daughters won’t be attacked.”

Eliasson said he would be very surprised if water, sanitation and hygiene did not figure “very highly” in the SDGs. “[It’s] such a good investment: invest in sanitation and you will have concrete results with positive changes for people’s lives,” he said. “The economic losses are tremendous and the economic gains are enormous.”

“It’s most often the poor people who move into the urban, sprawling areas of poor countries, and the infrastructure does not exist, and the collective water and sanitation arrangements are not made,” he said. “That’s when you have the big risks of outbreaks of diarrhoea and dysentery.”

Asked what the consequences of any further inaction would be for the hundreds of millions of people still in desperate need of a clean and safe place to defecate, he was blunt: “They would be disastrous. We simply have to do this.”

‘A world of toilets for all’

The international coalition seeking to break the taboos around the twin issues of toilet provision and open defecation is an unlikely one, comprising among others, a 73-year-old Swedish diplomat, the government of Singapore and a bright green Sesame Street resident by the name of Raya.

Eliasson has long campaigned for improved sanitation. Sometimes, he reflects, undiplomatic language is called for.

“I remember I finished a speech once, where the original text was, ‘We have to work for a life of dignity for all’. And that was code language for sanitation,” he says. “I changed that line to: ‘We have to work for a world of toilets for all’. I can tell you, there were lots of raised eyebrows and confusion in the translators’ booths.”

Eliasson says things have moved on since, especially as the term open defecation – “which is a euphemism in itself” – entered diplomatic discourse.

Credit, he says, must also go to Singapore, which last year successfully proposed that the UN designate 19 November as World Toilet Day as a way of focusing global attention on sanitation issues.

Toilets at a petrol station near Accra, Ghana. Photograph: David Levene for the Guardian

“We need more toilets,” she told the UN in May. “With more toilets in schools and pledges around the world, we can stop millions of children and grown-ups from getting sick. Then we can remind everyone to wear shoes and sandals when they go to the toilet … and to wash their hands.”